In most internal combustion engines, it is desirable to maintain pressure within the engine crankcase below atmospheric pressure thereby reducing leaks through gaskets and seals from the crankcase to the atmosphere. This is normally done by evacuating crankcase blowby gases through a breather system driven by a vacuum source.
In most cases, it is not desirable for the crankcase vacuum (i.e. negative crankcase pressure) to become excessive. If the crankcase vacuum is excessive, or if crankcase seals deteriorate, the vacuum can pull in outside air and dirt across the seals. For internal combustion engines, it is therefore preferred to maintain a slight crankcase vacuum. The magnitude of the vacuum should not vary excessively with such factors as engine speed or load, engine wear, or other factors which may affect the operation of the crankcase breather system.
The invention provides a crankcase pressure regulation system that can maintain negative crankcase pressure within narrow tolerances. The invention does this by adjusting the volumetric flow rate through the breather system.
The invention involves creating a negative pressure in the crankcase by drawing blowby gas from the crankcase and regulating the negative crankcase pressure by adding a regulated amount of air to the flow of the blowby gas drawn from the crankcase and thereafter restricting the combined flow. Since pressure losses across flow restrictions increase at a rate proportional to the square of volumetric flow through the restriction, the vacuum or pressure gradient drawing a flow of blowby gas from the crankcase can be precisely controlled by adding a relatively small amount of ambient air to the flow of blowby gas.
It is preferred that the regulated vacuum or pressure gradient drawing the flow of blowby gas from the crankcase be driven by a pressure drop across an engine air filter that is created by filtering engine intake air through the air filter. Such a system is advantageous because in such a system crankcase blowby gases are recirculated into the engine air intake for combustion, rather than being exhausted to the atmosphere. Because of the recirculation, ambient air added to the flow of blowby gas should be filtered.
This method of crankcase pressure regulation has many other advantages, one of which is that the system can be used with either low-pressure or high-pressure fuel systems, or with naturally aspirated or turbocharged engines.
The invention can be embodied in an improved crankcase pressure regulation system for an internal combustion engine burning gaseous fuel, but can also be used in liquid or slurry burning engines. The system can be used in an engine with a crankcase having a breather port through which crankcase blowby gases exit. The system includes a breather tube having an inlet that receives the crankcase blowby gases exiting the breather port and an outlet that feeds the blowby gases into an air intake housing where the blowby gases are mixed with filtered intake air. The pressure in the air intake housing is less than the atmospheric pressure because of the pressure drop across the air filter, and this pressure drop draws the blowby gases into the housing. A flow restriction, such as an oil separator, is located along the breather tube and a vacuum pressure regulator, preferably a floating-disk type vacuum pressure regulator, is operatively connected to the breather tube, preferably upstream of the oil separator. This system not only recirculates the blowby gases into the engine for combustion, but also provides a cost effective manner for maintaining slight negative crankcase pressure within narrow tolerances.